Automatic toner control system



Om. 24, 1967 .1. M. DONOHUE 3,343,522

-AUTOM1\TIC TONER CONTROL SYSTEM Filed April 7, 1965 4 Sheets-Sheet 1 INVENTOR JAMES M. DONOHUE was 9 wfi? J. M. DONOHUE AUTOMATIC TONER. CONTROL SYSTEM 4 Sheets-Sheet 2 Filed April 7, 1965 INVENTOR. JAMES M. DONOHUE ATTORNEYS ct. 24, 1967 J. M. DONOHUE 3,343,522

AUTOMATIC TONER CONTROL SYSTEM Filed A ril 7, 1965 4 Sheets-Sheet 5 FIG; 1/ FIG, [0 JAMES mf zl -fibli ATTORNEYS ct. 24, 1967 J. M. DoNoHu 3,343,522

AUTOMATIC TONER CONTROL SYSTEM Filed April 7, 1965 4 sheets-sheet 4 v 2 v5 g IOLS v 276 i 47 I i 246 I 245 .SH/ l sma 'INVENTOR.

JAMES M. DONOHUE A TTORNEVS United States Patent Ofiice 3,343,522 Patented Oct. 24, 1967 York Filed Apr. 7, 1965, Ser. No. 446,350 3 Claims. (Cl. 1187) ABSTRACT OF THE DISCLOSURE Apparatus for controlling the amount of toner dispensed in a developer mechanism in response to the quality of an image developed therein.

This invention relates to improvements in toner dispensing devices and, particularly, to improvements in the automatic control of these devices to facilitate the making of xerographic reproductions.

The present invention avoids the disadvantages of manual control for dispensing toner particles into the developing material used in xerographic processing equipment. This method of control is generally based upon guess work by the operator who must continually observe the reproduction copy quality in contrast in order to maintain a reproduction run that is fairly constant in regard to image contrast. For automatic xerographic processing wherein large production runs are frequent, an experienced operator must be in attendance to insure good quality contrast.

Therefore, the principal object of the invention is to automatically control toner dispensing in Xerographic processing systems. A further object of the invention is to improve image contrast quality for Xerographic processing systems.

These and other objects of the invention are attained by means of control circuit utilized in conjunction with an improved toner dispensing device for dispensing toner into the developing apparatus in accordance with the density of a developed image upon the Xerographic plate. Means are provided for producing an elastrostatic image on the plate. This image is developed along with the image of a document being reproduced by the xerographic machine. A sensing device is also provided for scanning the developed image and determining the density of this image. This determination is accomplished electrically by a bridge circuit which includes photocells arranged to receive light rays emanating from the development image and to compare electrically the light values relative to standard conditions. The resultant effect upon the bridge circuit is utilized to actuate the toner dispensing device for adding toner to the developing material, if needed.

A preferred form of the invention is shown in the accompanying drawings in which:

FIG. 1 is a schematized sectional view of a Xerographic machine embodying the principles of the invention;

FIG. 2 is an isometric view of a toner dispenser utilized with the xerographic machine;

FIG. 3 is a front view of the toner dispenser and its actuating mechanism;

FIG. 4 is a sectional view of the stripe marker for the automatic toner dispensing circuit;

FIG. 5 is a sectional view of the stripe light mask taken along line 55 in FIG. 4;

FIG. 6 is a sectional view of the light mask taken along the line 66 in FIG. 4;

FIG. 7 is an illustration of a developed powder image of the stripe produced by the toner dispensing control system;

FIG. 8 is an enlarged view of the sensing head used to sense the density of the developed powder image;

FIG. 9 is a left hand view of the sensing head as it appears in relation to the Xerographic drum surface;

FIG. 10 is a schematic wiring diagram of the sensing head apparatus;

FIG. 11 is a wiring diagram for controlling the dispenser motor; and

FIG. 12 is a schematic illustration of the drive mechanism for the toner dispenser.

For a general understanding of the Xerographic processing system in which the invention is incorporated, reference is had to FIG. 1 in which the various system components are schematically illustrated. As in all xerographic systems, a light image of copy to be reproduced is projected onto the sensitized surface of a xerographic plate to form an electrostatic latent image thereon. Thereafter, the latent image is developed with an oppositely charged developing material to form a xerographic powder image, corresponding to the latent image, on the plate surface. The powder image is then electrostatically transferred to a support surface to which it may be fused by a fusing device, whereby the powder image is caused permanently to adhere to the support surface.

In the system disclosed herein, minified data cards are placed in the card magazine from which they are fed seriatim to a card carriage in a card handling apparatus, generally designated by reference character 11. Suitable driving means are provided for the card carriage whereby it is caused to move the card past the optical axis of a light projecting system to be described hereinafter for the purpose of scanning the minified data across a scanning light line. The illuminated card is projected downwardly by means of an objective lens assembly 12 and through a variable slit aperture assembly 13 and onto the surface of a xerographic plate in the form of a drum 14.

The xerographic drum 14 includes a cylindrical member mounted in suitable bearings in the frame of the machine and is driven in a counterclockwise direction by a motor at a constant rate that is proportional to the scan rate for the minified data card, whereby the peripheral rate of the drum surface is identical to the rate of movement of the reflected light image. The drum surface comprises a layer of photoconductive material on a conductive backing that is sensitized prior to exposure by means of a screened corona generating device 15.

The exposure of the drum to the light image discharges the photoconductive layer in the areas struck by light, whereby there remains on the drum a latent electrostatic image in image configuration corresponding to the light image projected from the minified data card. As the drum surface continues its movement, the electrostatic latent image passes through a developing station A in which there is positioned a developer apparatus including a casing or housing 16 having a lower or sump portion for accumulating developing material. A bucket-type conveyor having a suitable driving means, is used to carry the developing material to the upper part of the developer housing where it is cascaded down over a hopper chute onto the xerographic drum.

As the developing material is cascaded over the xerographic drum, toner particles are pulled away from the carrier component of the developing material and deposited on the drum to form powder images, while the partially denuded carrier particles pass off the drum into the developer housing sump. As toner powder images are formed, additional toner particles must be supplied to the developing material in proportion to the amount of toner deposited on the drum. For this purpose, a toner dispenser generally designated 17 is used to accurately meter toner to the developing material.

Positioned next and adjacent to the developing station is the image transfer station B which includes a sheet feeding mechanism adapted to feed sheets of paper successively to the developed image on the drum at the transfer station. This sheet feeding mechanism, generally designated 18, includes a sheet source such as a tray 20 for a plurality of sheets of a suitable transfer material that is typically, sheets of paper or the like, a separating roller adapted to feed the top sheet of the stack to feed rollers which direct the sheet material into contact with the rotating drum at a speed preferably slightly in excess of the rate of travel of the surface of the drum in coordination with the appearance of the developed image at the transfer station. In this manner, the sheet material is introduced between the feed rollers and is thereby brought into contact with the rotating drum at the correct time and position to register with the developed image. To effect proper registration of the sheet transfer material with the feed rollers and to direct the sheet transfer material into contact with the drum, guides are positioned on opposite sides of the feed rollers.-

The transfer of the xerographic powder image from the drum surface to the transfer material is effected by means of a corona transfer device 21 that is located at or immediately after the point of contact between the transfer material and the rotating drum. The corona transfer device 21 is substantially similar to the corona discharge device 15 in that it includes an array of one or more corona discharge electrodes that are energized from a suitable high potential source and extend transversely across the drum surface and are substantially enclosed within a shielding member.

In operation, the electrostatic field created by the corona discharge device is effective to tack the transfer material electrostatically to the drum surface, whereby the transfer material moves synchronously with the drum while in contact therewith. Simultaneously with the tacking action, the electrostatic field is effective to attract the toner particles comprising the xerographic powder image from the drum surface and cause them to adhere electrostatically to the surface of the transfer material.

Immediately subsequent to the image transfer station is positioned a transfer material stripping apparatus or paper pick-off mechanism, generally designated 22, for removing the transfer material from the drum surface. This device includes a plurality of small diameter, multiple outlet conduits of a manifold that is supplied with pressurized aeriform fluid through the outlet conduits into contact with the surface of the drum slightly in advance of the sheet material to strip the leading edge of the sheet material from the drum surface and to direct it onto a horizontal conveyor 23 having an endless conveyor 24 whereby the sheet material is carried to a fixing device in the form of a fuser assembly 25, whereby the developed and transferred xerographic powder image on the sheet material is permanently fixed thereto.

After fusing, the finished copy is preferably discharged from the apparatus at a suitable point for collection externally of the apparatus. To accomplish this there is provided a vertical conveyor, generally designated 26, by means of which the copy is delivered to a copy' holder positioned in a suitable super-structure overhanging the rear portion of the desk top.

The next and final station in the device is a drum cleaning station C, having positioned therein a corona precleaning device similar to the corona charging device 15, to impose an electrostatic charge on the drum and residual powder adherent thereto to aid in effecting removal of the powder, drum cleaning device adapted to remove any powder remaining on the xerographic drum after transfer and a source of light, not shown, whereby the xerographic drum is flooded with light to cause dissipation of any residual electrical charge remaining on the xerographic drum.

, In general, the electrostatic charging of the xerographic drum in preparation for the exposure step and the electrostatic charging of the support surface to effect transfer are accomplished by means of corona generating devices whereby electrostatic charge on the order of 500 to 60-0 volts is applied to the respective surface, in each instance. Although any one of a number of types of corona generating devices may be used, a corona charging device of the type disclosed in Vyverberg Patent 2,836,725 is used for both the corona charging device 15 and the corona transfer device 21, each of which is secured to suitable frame elements of the apparatus and connected to an electrical circuit described hereinafter.

As the developing mixture is cascaded over the xerographic drum, toner particles are pulled away from the carrier and deposited on the drum to form powder images, while the partially denuded carrier particles pass off the drum into the reservoir. As toner powder images are formed, additional toner particles must be supplied to the developing mixturein proportion to the amount of toner deposited on the drum. To supply additional toner particles to the developing mixture, the toner dispenser 17 is used to accurately meter toner to the developer mixture. Although any one of a number of well-known powder or granulated material dispensers may be used, the toner dispenser shown is of the type disclosed in Patent No. 3,062,109, issued November 6, 1962, to Mayo et al.

Referring now to FIGS. 2 and 3 the toner dispenser 17 consists of a hopper or container 220 for the toner particles to be dispensed. Although the hopper or container 220 may be made in any size or shape, the hopper shown is formed as a rectangular open-ended box having vertical side walls 221 and end walls 222, the upper ends of the walls being bent outward to form horizontal flanges by means of which the hopper may be attached to the underside of top wall 201 of the developer housing as by welding, with the opening in top wall 201 of the developer housing in alignment with the opening in the hopper. At opposite ends of the hopper are positioned depending bearing blocks 223 and 224 for supporting the remaining elements of the toner dispenser, the bearing blocks being attached to end walls 222 by screws 225.

The bottom of the hopper is partially closed by a dispensing plate 226 positioned in spaced vertical relation below the lower edges of the walls of the hopper. The dispensing plate 226 which is as wide as the hopper, is secured to the underside stepped portions of bearing blocks 223 and 224 by screws 227. The dispensing plate 226 combines with the walls of the hopper 220 'to provide a reservoir having narrow elongated outlet slits or passages 228 for the flow of toner particles.

To effect substantially uniform flow of toner particles through the outlets or passages 228 there is provided a metering element, generally designated 230, having a dispensing grid 231 positioned for reciprocating motion in the space between the dispensing plate 226 and the lower edges of the walls of the hopper 220. The metering element 230, as shown, has the dispensing grid 231 formed by a top wall having a series of transverse perforations or slots formed therein, and depending side walls 232, the ends of which are bent inward at right angles to form flanges 233 to which support plates 234 are secured as by spot welding. For ease and economy in manufacturing the metering element is formed as a sheet metal stamping, the slots being formed relatively close to each other and to the transverse edges of the top wall so that after the slots are formed there remains only narrow strips of metal simulating wires 235, the width of the metal remaining between slots being only sufficiently wide to prevent them from being bent out of shape in the stamping process.

The metering element 230 is supported by parallel guide rods 236 extending through holes formed in support plates 234, the ends of the guide rods being j'ournaled for reciprocating motion in apertures 237 formed in bearing blocks 223 and 224. As seen in FIG. 2, the movement of the guide rods 236 to the left is limited by collars 238 adjustably secured thereto by suitable screws, while movement of the metering element 230 with respect to the guide rods 236 is prevented by a second set of collars 240 secured by set screws to the guide rods inboard of the support plates 234.

For effecting movement of the metering element, a plunger rod 241 is journaled for reciprocating movement in a bearing block 242 secured to a side wall of the developer housing, the plunger extending at one end through a suitable aperture in the side wall to be actuated by a suitable power source, and at its opposite end the plunger rod extends through a suitable aperture in bearing block 223 into contact with the left-hand support plate 234. To limit the movement of plunger rod 241, retaining rings 243 are secured in suitable grooves at each end of the plunger rod. The return stroke of the metering element is effected by coiled springs 244 encircling the guide rods 236 and butting at opposite ends against the bearing block 224 and the right-hand support plate 234 to bias the metering element to the left.

As shown, the dispensing grid is positioned between the dispensing plate 226 and the lower edge of the walls of the hopper 220 in spaced relation to each other to permit free reciprocating movement of the grid. The space or clearance between each of the last-named elements may be varied during fabrication to accommodate the particle size of toner to be dispensed.

In the operation of the toner dispenser a supply of toner particles is placed within the hopper, the hopper grid and the dispensing plate forming a reservoir for the toner particles. Upon reciprocation of the grid by the plunger rod 241, a metered quantity of toner particles will be permitted to cascade through the open grid work of the grid from Where they will fall to the reservoir portion of the conveyor housing 16.

Since the toner dispenser 16 dispenses a uniform quantity of toner for a given stroke length of the metering element 230 it is apparent that the quantity of toner delivered by the toner dispenser may be varied by either varying the length of stroke or by varying the number of strokes per unit of time. Thus, the dispensing rate may be varied bychanging the length of stroke of the metering element 230, which, for example, may be accomplished in its simplest form by adjustment of the right-hand collars 240 on the grid rods 236.

Reciprocation of the plunger rod 241 is effected by means of wobble plate 245 secured to the end of a shaft SHlS journaled in bearings mounted on frame plates 5 and 215. The shaft is driven by a pulley connected by a belt to the shaft of a motor M7. The contour of the wobble plate 245 is such that one complete revolution of the shaft SHIS will actuate the rod 241 axially to reciprocate the dispensing grid once from one extreme position to the other.

In order to control the dispensing of toner from the toner dispenser 17 there is shown in FIGS. 4-10 the details of an automatic toner control system which ultimately imparts rotation to the wobble plate 245 in single revolution step by step operation in accordance with the density of the developed image on the drum 14. Basically, the automatic toner dispensing system comprises an exposure device which exposes a stripe along the edge of the drum after it is charged; a sensing device for generating a signal in accordance with the relative density of the developed stripe and; an electrical circuit for utilizing the signal for imparting rotation to the wobble plate of the toner dispenser.

As shown in FIG. 1, a stripe exposure or marking device 250 is mounted on the machine at a point between the charging device 15 and the developing mechanism 16. Between the transfer station 21 and the pre-cleaning device 27, there is mounted a sensing head 251 which is adapted to project light onto the developed stripe and to sense the density of the toner comprising the stripe in accordance with the light reflected from the stripe.

The stripe marking device 250 comprises a tubular member 252 secured above the drum to the interior of the housing 196, and is positioned with its axis projecting downwardly toward the drum 14. At the lower end, the tubular member is formed with an open end 253 which is closely spaced from the peripheral surface of the drum and slightly contoured to conform to the shape of the drum. Across the lower end 253 there is secured a narrow opaque strip of material 254 which covers approximately one-third of the otherwise open end 253 and is centrally located relative to this end for separating two open sectors 255 between the strip and the wall of the member 252. The sectors 255 are, in effect, windows for permitting exposure of the drum therethrough by means of a small lamp LMP-25 mounted within the member 250. The windows 255 are generally of equal area and, when the lamp is energized, allow the light rays therefrom to impinge the drum surface to expose that portion of the drum immediately below the windows. The strip 254 and windows 255 in effect, function as a mask which results in the formation of a stripe 256 of unexposed drum surface between two exposed areas 257, being produced when the lamp LMP25 is energized.

For efiicient operation of the automatic toner dispenser, the stripe marking device is located at one of the extreme ends of the drum 14 remote from the adjacent edge for the copy image area that evolves from use of the drum in the .xerographic machine. With this arrangement there 15 no interference between the exposure elements and the development of the resultant stripe pattern with the exposure elements for the xerographic processing. The exposure slit formed in the masking element 198 will not interfere with the operation of the marker device 250 and, conversely, the marking device will not interfere with the normal operation of the element 198. The only common operative inter-action between these two exposure devices is the use of the developer mechanism 16 for developing the respective images.

For a more accurate control of the toner dispenser and the surveilance of the resulting toner density, it is preferred that the stripe 256 produced on the drum have a length approximately one-fourth the circumference of the drum. It is also preferred that there be produced a series of three stripes for each revolution of the drum 14.

After the stripes 256 have been developed in the devel oper mechanism to formtoner powder images of the stripes, the stripes are transported by normal rotation of the drum 14, past the sensing device 251. In traveling to th1s point, the toner powder images of the stripes being formed adjacent one end of the drum 14, will be clear of the transfer station 21 and will not be transferred to a support material as is the case for the developed images of the data area of a card.

The sensing device 251 is mounted on a channel member 257 secured to the lower wall of the brush drum cleaning device 28 and includes a support block 258 having a wall surface 260 disposed in a plane at a slight angle relative to the adjacent surface of the drum. One end of a light transmitting fiber bundle 261 is mounted on the block- 258 with the end face 262 of the bundle flush with the plane of the wall surface 260. The other end of the fiber bundle projects out of the member 257 and terminates in the end Wall 263 of a cylindrical light shield 264 secured to the rear wall of the channel member 257. A lamp LMP-3, also secured to the rear wall of the member 257, extends into the shield 264 and, when energized, is adapted to present light rays upon the adjacent end face of the fiber bundle 261. The light rays, transmitted by the bundle 261, emerge from the end face 262 and, are directed to the stripe image on the drum surface at an angle relative thereto. In order to eliminate the possibility of spurious light reaching the drum surface and effecting the toner powder image of the stripes,

the fiber bundle 261 is covered with a suitable opaque sheath. One purpose for the fiber bundle is to avoid the effects of heat from a light source, such as the lamp LMP3 that would otherwise be mounted in closed proximity to the drum, which, if made of selenium would gradually crystallize in those areas constantly heated by the lamp. Another purpose is to avoid the possibility that the developing material may adhere to a closely positioned hot lamp and thereby interfere with proper illumination.

The support block 258 is also formed with two sideby-side apertures 265, 266 immediately below the end face 262 of the fiber bundle and positioned such that one aperture is on one side of the vertical center line for the end face. Mounted with the apertures are photoelectric devices or photocells P-2, P-3, respectively, which are adapted to scan the light rays reflected from the drum surface and directed thereon by the light rays emanating from the end face 262. The relative positioning of the photocells are such that the cell P-2 will receive the light rays or rather, the shadow of the developed stripe 256, illustrated in FIG. 9 by the dotted shadow 267. The cell P'3 is positioned to receive the light rays by reflection from one of the tonerless clear areas 257 and, consequently, will receive more reflected light rays than the cell P-2. In effect, the cell P3 will serve as a standard since the light it receives will remain constant through continuous use of the xerographic drum 14, while the light reaching the cell P-2 will vary in accordance with the density or amount of toner particles adhering to the drum along the stripe 256.

Electrically, the photocells P2, P-3 form two legs of a bridge circuit which is illustrated in FIG. and schematically shown in FIG. 9. The other two legs of the bridge circuit comprise two fixed resistors 268, 269 and portions of a variable resistor R-25 having its wiper arm 271 connected to the negative terminal of a DC. source 272. To complete the bridge circuit, the junction between the photocells is connected to the positive terminal of the DC. source. The power supply for the bridge circuit is derived from a DC. source 273 and potentiometer 274 which has its wiper arm connected between the resistor 268 and the photocell P-Z. The bridge unbalance output is fed to a Schmitt trigger 275 which, when energized, produces a short duration pulse to de-energize a normally energized relay TCR. As shown in FIG. 11, de-energization of the relay will permit actuation of a normally closed contact TCR-l to its closed position to complete the circuit momentarily to a relay coil 9CR. This causes closing of the relay contact 9CR-1 for closing the circuit to the motor M7 and energization thereof. Mounted on the shaft SH18 for rotation with the wobble plate 245 is a circular cam 276 adapted to actuate a normally closed limit switch 10LS to an open position once each revolution of the cam and wobble plate. Closing of the contact 9CR-1 also completes the circuit to the relay 90R for holding the contact closed until the wobble plate makes one complete revolution. Upon this occurrence, the switch l'tlLS is opened momentarily to de-energize the relay 9CR and to open the power circuit to the motor M7. Since a short duration pulse closed the contact TCR1 for initiating the motor M7 operation, this contact will be opened before the switch 10LS is opened.

During normal operation of the automatic toner dispensing apparatus, the sensing head lamp LMP-3 is continuously energized for presenting light upon the stripe 256 and adjacent clear areas 257. This light. is fairly evenly distributed upon these areas of the drum and the light reflected from the stripe and clear areas are sensed by the photocells P-2, P-3 and compared by the bridge circuit. The resistor R-25 is adjusted so that there is a bridge balance with zero output between the results of the light impinging upon the cell P-2 from the stripe 256 and the results of the light impinging upon the cell P-3 from one of the clear areas 257. This balance will be determined by the desired density .of the toner that adheres to the stripe 256. With a balanced condition of the bridge the Schmitt trigger will have zero output for the relay TCR. As the toner supply in the developer housing 16 depletes during normal xerographic processing, the density of the toner on the continuously sensed stripe 256 Will lessen. With a density lower than the predetermined level which was used to balance the bridge circuit, the bridge will swing out of balance and when differential current in the trunks of the bridge is sufliciently high, the Schmitt trigger, which, in effect is a level detector, will produce an electrical pulse causing a momentary deenergization of the relay TCR and closing of the relay contact TCR-l. For each electrical pulse produced in this manner, the wobble plate 245 will rotate one complete revolution by means of the drive belt 247 and pulley 246. As previously stated, one revolution of the plate 245 will actuate the dispensing grid 241 between its extreme position for dispensing toner into the developer housing.

As the density of the toner on the stripe 256 increases, the balance of the bridge circuit will become restored thereby terminating further actuation of the toner dispenser. The sensitivity of the sensing head can be varied by the parameters chosen for the resistors 268, 269 and R-25 and the strength of the DC. sources 272, 273. These components will determine the output level of the bridge circuit and may be varied so that a high unbalance must be present before a level can be detected by the Schmitt trigger. This condition would evolve that it is desirable to have a relatively wide density range for xerographic reproductions. If high quality contrast is needed in the reproductions, then a very sensitive bridge balance is necessary whereby the slightest unbalance will demand toner dispensing and replenishment.

The toner dispenser 17 functions to sift toner material onto the developing material already present in the developer housing. In order to ensure uniform distribution of new toner to bring the toner density back to the desired level in a minimum of time, the toner dispenser extends horizontally substantially across the upwardly moving buckets which are in motion to cascade toner over the drum surface throughout its entire width.

Some of the newly dispensed toner may be caused to deposit on suitable baffle plates. To cause these particles to be mixed with the remaining developing material and thereby ensure adequate mixing of at least a portion of the new toner, narrow slots maybe formed in these plates whereby a portion of the material sliding down this plate is caused to pass through the slots and over the surface of the developing material supply at the bottom of the housln'g.

While the invention has been described with reference to the structure disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.

What is claimed is:

1. A toner dispensing device and control circuit therefor for use in an electrostatic reproduction apparatus having an electrostatic reproducing plate and a developer mechanism adapted to apply developer material to exposed images on the plate thereby producing powdered images thereon including:

a container for the toner,

means for dispensing toner from the container into the developer mechanism for replenishing the developing material with toner,

an actuator device associated with the said dispensing means for controlling the introduction of the toner into the developer mechanism,

means for producing on a portion of the electrostatic reproducing plate remote from the exposed image to be reproduced an electrostatic image for development by the developer mechanism,

a light source arranged for illuminating the developed image,

a light sensitive device arranged to receive the light rays from said image and to produce an output in accordance therewith,

means for comparing said output with a preset output and producing a dilierential signal,

and means responsive to said differential signal and associated with said dispensing means for actuating the same to dispense toner into the developer mechanism.

Z. A toner dispensing device and control circuit therefor for use in an electrostatic reproduction apparatus having an electrostatic reproducing plate and a developer mechanism adapted to apply developer material to exposed images on the plate thereby producing powdered images thereon including:

a container for the toner,

means for dispensing toner from the container into the developer mechanism for replenishing the developing material with toner,

an actuator device associated with the said dispensing means for controlling the introduction of the toner into the developer mechanism,

means for producing on a portion of the electrostatic reproducing plate remote from the exposed image to be reproduced an electrostatic image for develop ment by the developer mechanism,

a light source arranged for illuminating the developed image,

a light sensitive device arranged to receive the light rays from said image and connected in a bridge circuit electrically in balance when the density of the developed image is at a predetermined value and unbalanced when the density falls below said predetermined value,

said bridge circuit being adapted to produce an output when unbalanced,

and means associated with said bridge circuit for actuating the dispensing means for dispensing toner into the developer mechanism when the bridge becomes unbalanced.

3. In a reproducing apparatus of the type wherein an electrostatic reproducing plate is charged, exposed and developed, a toner dispensing device for controlling the toner concentration in a developer mechanism adapted to apply developing material to exposed images on the plate thereby producing powdered images thereon including means to produce an electrostatic control latent image on a remote area of the plate prior to its passing through the developer mechanism,

a container for toner particles means for dispensing toner particles from the container into the developer mechanism for replenishing the developing material,

an actuator device associated with said dispensing means for controlling the introduction of the toner particles into the developer mechanism,

a light source arranged to illuminate the developed control image on the plate after development,

a first light sensitive device being capable of receiving the light rays from the developed control image,

a second light sensitive device being adapted to receive light rays from an undeveloped portion of said remote area,

means for comparing the outputs of said first and second light sensitive devices and producing dilTerential signal thereof,

and means responsive to said differential signal and associated with said dispensing means for actuating the same to dispense toner into the developer mechamsm.

References Cited UNITED STATES PATENTS 5/1960 Giaimo l.7 6/1963 Snelling 118-637 X 2/1966 Grubbs 1l8-9 X 

1. A TONER DISPENSING DEVICE AND CONTROL CIRCUIT THEREFOR FOR USE IN AN ELECTROSTATIC REPRODUCTION APPARATUS HAVING AN ELECTROSTATIC REPRODUCING PLATE AND A DEVELOPER MECHANISM ADAPTED TO APPLY DEVELOPER MATERIAL TO EXPOSED IMAGES ON THE PLATE THEREBY PRODUCING POWDERED IMAGES THEREON INCLUDING: A CONTAINER FOR THE TONER, MEANS FOR DISPENSING TONER FROM THE CONTAINER INTO THE DEVELOPER MECHANISM FOR REPLENISHING THE DEVELOPING MATERIAL WITH TONER, AN ACTUATOR DEVICE ASSOCIATED WITH THE SAID DISPENSING MEANS FOR CONTROLLING THE INTRODUCTION OF THE TONER INTO THE DEVELOPER MECHANISM, MEANS FOR PRODUCING ON A PORTION OF THE ELECTROSTATIC REPRODUCING PLATE REMOTE FROM THE EXPOSED IMAGE TO BE REPRODUCED AN ELECTROSTATIC IMAGE FOR DEVELOPMENT BY THE DEVELOPER MECHANISM, A LIGHT SOURCE ARRANGED FOR ILLUMINATING THE DEVELOPED IMAGE, A LIGHT SENSITIVE DEVICE ARRANGED TO RECEIVE THE LIGHT RAYS FROM SAID IMAGE AND TO PRODUCE AN OUTPUT IN ACCORDANCE THEREWITH, MEANS FOR COMPARING SAID OUTPUT WITH A PRESET OUTPUT AND PRODUCING A DIFFERENTIAL SIGNAL, AND MEANS RESPONSIVE TO SAID DIFFERENTIAL SIGNAL AND ASSOCIATED WITH SAID DISPENSING MEANS FOR ACTUATING THE SAME TO DISPENSE TONER INTO THE DEVELOPER MECHANISM. 